The second
edition of Gauge Theories of the Strong, Weak, and Electromagnetic
Interactions, published by Princeton University Press, is now
available. See the Illustration Package (digital versions of the figures) for classroom use.

Particle Physics!

Our theories of the
fundamental particles and the interactions among them are in a very
provocative state. We have achieved a simple and coherent understanding of
an unprecedented range of natural phenomena, but our new understanding
raises captivating new questions. In search of answers, we have made
far-reaching speculations about the universe that may lead to revolutionary
changes in our perception of the physical world, and our place in it. We
are experiencing a remarkable flowering of
experimental particle physics and of theoretical physics that engages with
experiment!

The Large Hadron Collider at CERN is advancing the
experimental frontier of particle physics to the heart of the Fermi scale, reaching
energies around one trillion electron volts for collisions among the basic constituents
of matter. We do not know what the new wave of exploration will find, but
the discoveries we make and the new puzzles we encounter are certain to change
the face of particle physics and echo through neighboring
sciences.

In this new world, we confidently expect to learn what distinguishes electromagnetism
from the weak interactions, with profound implications for our conception
of the everyday world. We will gain a new understanding of simple and profound
questions: Why are there atoms? Why chemistry? What makes stable structures
possible? A pivotal step is the discovery of a Higgs boson and the elaboration
of its properties. But there may be much more: we have hints of other new
phenomena, including some that may clarify why gravity is so much weaker than
the other fundamental forces. We also have reason to believe that candidates for
the dark matter of the Universe could be lurking on the Fermi scale.

Beyond the Fermi scale lies the prospect of other new insights: into the different
forms of matter, the unity of quarks and leptons, and the nature of spacetime. The
questions in play all seem linked to one another—and to the relationship of the
weak and electromagnetic interactions. Exploring the Fermi scale will help us to
define the questions more acutely, and may set us on the road to answering
them.

Experiments of exquisite sensitivity, in which new physics may manifest
itself through quantum corrections, provide an essential complement to
the LHC research program and give us a virtual look at even
higher energy scales. Many initiatives promise to develop our
understanding of the problem of identity: what makes a neutrino a neutrino
and a top quark a top quark. Here I have in mind the work of the
e+e- flavor factories
and the LHC on CP violation and the weak interactions of the
b and c
quarks; wonderfully sensitive experiments
on CP violation and ultrarare decays of kaons; the prospect of
definitive experiments on neutrino oscillations and the nature
of the neutrinos; and a host of new acclerator-based experiments to search for
nonconservation of lepton number or baryon number.

Experiments that use natural sources also hold great promise for the
decades
ahead. We suspect that the
detection of proton decay is only a few orders of magnitude away in
sensitivity. Astronomical observations
should help to tell us what kinds of matter and energy make up the universe.
The areas already under
development—if not exploitation—include gravity wave detectors,
neutrino telescopes, cosmic microwave
background measurements, cosmic-ray observatories, γ-ray astronomy,
and large-scale optical surveys.
Indeed, the whole complex of experiments and observations that we call
astro/cosmo/particle physics should
enjoy a golden age.

If we are inventive enough, we may be able to follow this rich
menu with the physics opportunities offered by a (muon-storage-ring) neutrino factory, a Higgs factory, a TeV-scale linear electron-positron collider or
muon collider, and a very-high-energy hadron collider.

Current Research

My work ranges over many topics in particle physics, from electroweak
symmetry breaking and supercollider physics to heavy quarks and the strong
interaction among them to ultrahigh-energy neutrino interactions. The
essential interplay between theory and experiment is a guiding theme.
Because we cannot hope to advance without new instruments, I have devoted
much energy to helping to define the future of particle physics—and
the new accelerators that will take us there.
Much of my current work is linked with the experimental program of the
Large Hadron Collider, with special attention to the problem of electroweak symmetry
breaking. I maintain an active interest in quarkonium
spectroscopy and the new mesons associated with quarkonium.